Shared Pixel Arrays with Dual Conversion Gain for High Dynamic Range
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Solution Overview
Problem
Standard CMOS image sensors have a limited dynamic range due to small pixel size, which restricts the capacitance of added capacitors in dual conversion gain (DCG) pixels, making it difficult to capture high dynamic range images effectively, especially in low light conditions.
Innovation Solution
The implementation of shared pixel arrays with dual conversion gain transistors and capacitors, where the capacitance is distributed across multiple photodiodes and a shared capacitor, allowing for adjustable conversion gain by switching between high and low gain modes to accommodate varying light conditions without increasing pixel size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pixel size is reduced to increase resolution, then the camera resolution increases, but the dynamic range decreases due to limited capacitor area
Solution Approach 1:
Multiple pixels share a single capacitor structure, combining the capacitance resources of multiple pixels into one shared component. This allows each pixel to utilize the full capacitance value despite the reduced physical area available in small pixels, thereby maintaining dynamic range while enabling higher resolution through smaller pixel dimensions.
Solution Approach 2:
The shared capacitor serves multiple pixels simultaneously, performing the same capacitance function for each pixel that would otherwise require individual dedicated capacitors. This multi-functional approach allows the system to maintain the required dynamic range performance across all pixels without proportionally increasing the total area allocated to capacitor structures.
2Adaptability or versatility
If a capacitor is added to the pixel circuit to provide low conversion gain, then dual conversion gain capability is achieved, but the area of the capacitor is limited due to small pixel size
Solution Approach 1:
Multiple pixels share a single capacitor structure, combining the capacitance resources of multiple pixels into one shared component. This allows each pixel to utilize the full capacitance value despite the reduced physical area available in small pixels, thereby maintaining dynamic range while enabling higher resolution through smaller pixel dimensions.
Solution Approach 2:
The capacitor is implemented using vertical stacking in the third dimension rather than expanding horizontally in the pixel plane. By utilizing the vertical space above the pixel circuit, the capacitor achieves sufficient capacitance value without consuming additional lateral area, thus preserving pixel density while enabling dual conversion gain functionality.
3Reliability
If the capacitance is increased to improve dynamic range, then the dynamic range increases, but the pixel size must be increased
Solution Approach 1:
Multiple pixels share a single capacitor structure, combining the capacitance resources of multiple pixels into one shared component. This allows each pixel to utilize the full capacitance value despite the reduced physical area available in small pixels, thereby maintaining dynamic range while enabling higher resolution through smaller pixel dimensions.
Solution Approach 2:
The capacitor is implemented using vertical stacking in the third dimension rather than expanding horizontally in the pixel plane. By utilizing the vertical space above the pixel circuit, the capacitor achieves sufficient capacitance value without consuming additional lateral area, thus preserving pixel density while enabling dual conversion gain functionality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the dynamic range of image sensors by allowing for larger capacitance in high gain mode and smaller capacitance in low gain mode, improving the differentiation of low light signals and reducing noise, thus capturing a wider range of luminance without increasing pixel size.
Implementation Method 1
A first pair of shared pixels comprises a first photodiode and a second photodiode
Data Source
AI summary
A group of shared pixels comprises: a first shared pixel comprising a first photodiode and a first transfer gate; a second shared pixel comprising a second photodiode and a second transfer gate; a third shared pixel comprising a third photodiode and a third transfer gate; a fourth shared pixel comprising a fourth photodiode and a first transfer gate; a first floating diffusion shared by the first shared pixel and the second shared pixel; a second floating diffusion shared by the third shared pixel and the fourth shared pixel; a capacitor coupled to the first floating diffusion through a first dual conversion gain transistor, and the second floating diffusion through a second dual conversion gain transistor; wherein the capacitor is formed in an area covering most of the first shared pixel, the second shared pixel, the third shared pixel, and the fourth shared pixel.